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bup(1)							      General Commands Manual							    bup(1)

bup - Backup program using rolling checksums and git file formats SYNOPSIS
bup [global options...] <command> [options...] DESCRIPTION
bup is a program for making backups of your files using the git file format. Unlike git(1) itself, bup is optimized for handling huge data sets including individual very large files (such a virtual machine images). However, once a backup set is created, it can still be accessed using git tools. The individual bup subcommands appear in their own man pages. GLOBAL OPTIONS
--version print bup's version number. Equivalent to bup-version(1) -d, --bup-dir=BUP_DIR use the given BUP_DIR parameter as the bup repository location, instead of reading it from the $BUP_DIR environment variable or using the default ~/.bup location. COMMONLY USED SUBCOMMANDS
bup-fsck(1) Check backup sets for damage and add redundancy information bup-ftp(1) Browse backup sets using an ftp-like client bup-fuse(1) Mount your backup sets as a filesystem bup-help(1) Print detailed help for the given command bup-index(1) Create or display the index of files to back up bup-on(1) Backup a remote machine to the local one bup-restore(1) Extract files from a backup set bup-save(1) Save files into a backup set (note: run "bup index" first) bup-web(1) Launch a web server to examine backup sets RARELY USED SUBCOMMANDS
bup-damage(1) Deliberately destroy data bup-drecurse(1) Recursively list files in your filesystem bup-init(1) Initialize a bup repository bup-join(1) Retrieve a file backed up using bup-split(1) bup-ls(1) Browse the files in your backup sets bup-margin(1) Determine how close your bup repository is to armageddon bup-memtest(1) Test bup memory usage statistics bup-midx(1) Index objects to speed up future backups bup-newliner(1) Make sure progress messages don't overlap with output bup-random(1) Generate a stream of random output bup-server(1) The server side of the bup client-server relationship bup-split(1) Split a single file into its own backup set bup-tick(1) Wait for up to one second. bup-version(1) Report the version number of your copy of bup. SEE ALSO
git(1) and the README file from the bup distribution. The home of bup is at <>. AUTHORS
Avery Pennarun <>. Bup unknown- bup(1)

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bup-margin(1)						      General Commands Manual						     bup-margin(1)

bup-margin - figure out your deduplication safety margin SYNOPSIS
bup margin [options...] DESCRIPTION
bup margin iterates through all objects in your bup repository, calculating the largest number of prefix bits shared between any two entries. This number, n, identifies the longest subset of SHA-1 you could use and still encounter a collision between your object ids. For example, one system that was tested had a collection of 11 million objects (70 GB), and bup margin returned 45. That means a 46-bit hash would be sufficient to avoid all collisions among that set of objects; each object in that repository could be uniquely identified by its first 46 bits. The number of bits needed seems to increase by about 1 or 2 for every doubling of the number of objects. Since SHA-1 hashes have 160 bits, that leaves 115 bits of margin. Of course, because SHA-1 hashes are essentially random, it's theoretically possible to use many more bits with far fewer objects. If you're paranoid about the possibility of SHA-1 collisions, you can monitor your repository by running bup margin occasionally to see if you're getting dangerously close to 160 bits. OPTIONS
--predict Guess the offset into each index file where a particular object will appear, and report the maximum deviation of the correct answer from the guess. This is potentially useful for tuning an interpolation search algorithm. --ignore-midx don't use .midx files, use only .idx files. This is only really useful when used with --predict. EXAMPLE
$ bup margin Reading indexes: 100.00% (1612581/1612581), done. 40 40 matching prefix bits 1.94 bits per doubling 120 bits (61.86 doublings) remaining 4.19338e+18 times larger is possible Everyone on earth could have 625878182 data sets like yours, all in one repository, and we would expect 1 object collision. $ bup margin --predict PackIdxList: using 1 index. Reading indexes: 100.00% (1612581/1612581), done. 915 of 1612581 (0.057%) SEE ALSO
bup-midx(1), bup-save(1) BUP
Part of the bup(1) suite. AUTHORS
Avery Pennarun <>. Bup unknown- bup-margin(1)
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